I have made the other mistake before. I have used the normal ip nat inside/outside interface commands and accidentally left the "inside" out of the "ip nat inside source statix x.x.x.x y.y.y.y" it does not work as expected. That is a little hard to spot. There are a few things (like stateful nat) that require the older method (using ip nat inside and ip nat outside, along with the related ip nat inside source static list x x.x.x command).